wetland

n. area of land that has wet soil (such as a marsh or bog)

In physical geography, a wetland is an environment "at the interface between truly terrestrial ecosystems and  aquatic systems making them inherently different from each other yet highly dependent on both" (Mitsch & Gosselink, 1986). In essence, wetlands are ecotones. Wetlands often host considerable biodiversity and endemism. In many locations such as the United Kingdom and USA they are the subject of conservation efforts and Biodiversity Action Plans.
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Land that stays flooded all or part of the year with fresh or salt water.

A lake, marsh, or swamp that supports wildlife and replenishes the groundwater system

Noun
1. a low area where the land is saturated with water
(hypernym) land, ground, soil
(hyponym) bog, peat bog